Chase mail/cclient shared library version bump.
Several patches were needed due to the removal of
include/c-client/linkage.c in favour of include/c-client/linkage.h.
PR: ports/114833
Submitted by: "Pedro J. Lobo" <pjlobo@sec.upm.es>

Redo the postilion port: - Don't use the imap library that comes with it --
use the cclient port. Don't even extract it. - Don't bother patching
configure and Makefile.in(s) -- use a local Makefile. - Use the latest
TCL/TK 8.3. This port does not provide any loadable packages, so I chose
not to use tclstubs, but link with libtk and libtcl directly. - Remove
the tkstep cruft -- it was commented out since forever. - Finally fix the
options.tcl -- the env(MAIL) logic was backwards.

(1) Add new variable, XFREE86_VERSION, to specify which version of XFree86
(3 or 4) to depend to when USE_XLIB is set. XFREE86_VERSION defaults to 3
for now, but adventurous users can override it in /etc/make.conf. When
XFREE86_VERSION=3, USE_XLIB will add a dependency to x11/XFree86; when it
is set to 4, the dependency will be to x11/XFree86-4-libraries. When
XFREE86_VERSION=4, the PKG_IGNORE_DEPENDS and ALWAYS_BUILD_DEPENDS hacks
to avoid messing with XFree86 are turned off.